1. Field of the Invention
The field of the invention is data processing, or, more specifically, methods, apparatus, and products for multi-layer printed circuit boards with through-hole vias.
2. Description of Related Art
The development of the EDVAC computer system of 1948 is often cited as the beginning of the computer era. Since that time, computer systems have evolved into extremely complicated devices. Today's computers are much more sophisticated than early systems such as the EDVAC. Computer systems typically include a combination of hardware and software components, application programs, operating systems, processors, buses, memory, input/output devices, and so on. As advances in semiconductor processing and computer architecture push the performance of the computer higher and higher, more sophisticated computer software has evolved to take advantage of the higher performance of the hardware, resulting in computer systems today that are much more powerful than just a few years ago.
One of the areas that has seen considerable development is PCB design, particularly as PCB bandwidths have advanced well into the gigahertz region. As electronic bandwidths expand, the impedances inherent in the conductive pathways on the PCBs themselves become relevant. When signal conductors change layers in multi-layer stackup applications, vias are used. However, when through-hole-vias are used for signal conductors to change layers, any unused via stub will hurt signal integrity. As frequency increases, signal performance is greatly impacted by reflections from those open stubs. A quarter-wave length resonance is particularly detrimental in high speed data transmissions. In current industry practice, termination methods using a resistor, an inductor or a capacitor are used to minimize those through-hole-via stub effects. However, the resistor termination results in undesired DC loss for the signal. The inductor/capacitor termination will shift the quarter-wave length resonance, but still have a resonance which can affect other frequency bands. Using those extra components requires real estate to mount those components which will eventually restrict the freedom of routability.